1. Field of the Invention
The present invention relates to method and apparatus for removing a composite attached to a material to be treated by a dry etching for use in a photo resist or a surface treatment of a semiconductor manufacturing process or the like.
2. Description of the Background Art
In a conventional apparatus for manufacturing a semiconductor or the like, it is important and essential to conduct a photo etching process (PEP) with an organic compound film such as a photosensitive photoresist as a mask in finely processing a printed circuit board, a compact disc or a laser disc. Then, this organic compound photoresist is removed after finishing a processing such as an etching and an ion-implanting of a main plate or board. The removal of the photoresist is mainly carried out in a wet chemical etching process, e.g., in a mixed solution of a sulfuric acid and a hydrogen peroxide or another mixed solution of the former mixed solution and water added thereto, or in a dry plasma etching process, e.g., in a dry ashing with oxygen gas dissociated by discharge.
In the wet chemical etching process, there are some problems in controlling the acidic solution and the safety of the operation. Particularly, this process is not suitable for a process for manufacturing a semiconductor which dislikes a process using a liquid, and further, when an organic compound photoresist is used for patterning a metallic electrode material such as aluminum or the like in a semiconductor producing process, the metallic electrode can be eaten easily by the acidic mixed solution of the sulfuric acid and the hydrogen peroxide. Thus, the application of the wet chemical etching process is restricted.
In the dry plasma ashing process which removes the problems of the wet chemical etching process, the organic compound photoresist can be removed in the dry ashing by the oxygen plasma. In this case, a material to be etched is placed in a barrel type or parallel plate type reactor, and the oxygen gas introduced therein is dissociated by the discharge therein to produce the oxygen plasma. The organic compound photoresist is removed using the oxygen plasma. In this process, as compared with the wet chemical etching process, the processing is conducted in a simple way and the material to be etched is not limited to the nonmetallic materials. However, in the dry plasma ashing method, the electric discharge is practiced in the reactor containing the material to be treated in order to attain a certain removing speed in practice, and hence the material is damaged on its surface or a resist residue is produced on the surface.
An example of a process for producing a gate electrode on a semiconductor plate of a MOS semiconductor device in a conventional photo etching process using an oxygen plasma will be described in connection with FIG. 1.
First, a phosphorus-added polycrystalline silicon film 3 for a gate electrode is formed on a semiconductor base plate 1 via an oxide film 2 formed thereon, and an organic compound photoresist film 4 is applied over the polycrystalline silicon film 3, as shown in FIG. 1a. Then, a pattern light exposure is carried out and is then developed so as to obtain the desired partial resist film 4a on the gate electrode film 3, as shown in FIG. 1b. By utilizing the partial resist film 4a as a mask, a partial gate electrode film 3a right under the partial resist film 4a is left by etching the other part of the polycrystalline silicon film 3 in the reactive ion etching (RIE) process or the like, as shown in FIG. 1c. Finally, the partial photoresist film 4a is removed from the polycrystalline film 3a in the dry plasma ashing process using the aforementioned oxygen plasma, as shown in FIG. 1d.
However, when the partial photoresist film 4a is removed from the gate electrode film 3a, as shown in FIG. 1d, the residues 5 of the ashed organic compound may be often produced on the surfaces of the gate electrode film 3a and the oxide film 2. Further, by the attack of the charged particles produced by the discharge during the removing step of the photoresist film 4a, the damages may be caused in the oxide film 2 and the semiconductor plate 1. Accordingly, in the MOS semiconductor device produced as described above, the residues 5 may affect bad influences to the followed processes or the characteristics of the semiconductor, for example, the resistivity of the oxide film may be deteriorated.
These problems arise in both the barrel type and the parallel plate type ashing reactors. In the latter reactor, the charged particles mainly impact against the surface of the material to be removed during the discharge, and thus the damage of the material is larger than that in the former reactor.
Further, in the oxygen plasma ashing process, usually, the charged particle such as oxygen radical and ozone does not react with the photoresist of the material to be removed at a practical speed at a low temperature such as below approximately 100.degree. C., and hence heat or another energy instead of the heat is added to the material placed in the plasma. When the material is heated, the inside of the photoresist is carbonized. Therefore, it is more difficult to remove the residues of the organic compounds exposed by the charged particles during the dry plasma ashing, and the residues are apt to remain on the surfaces of the material, in comparison with another process including no dry plasma ashing step.
In order to completely remove the residues 5, it is necessary to perform the oxygen plasma ashing for a long time, for instance, more than one hour, which is inconvenient and disadvantageous for realizing the manufacturing process, and further in such a long oxygen plasma ashing process, the damage to the material is enlarged. Then, the temperature in the reactor is raised to more than 100.degree. C. for improving the etching rate, but this requires a large and complicated processing apparatus. Further, in turn, the residues are liable to be produced at the high temperature, and the residues cannot be completely removed.
On the other hand, nowadays, a pattern size of an integrated circuit for a semiconductor is remarkably diminished to such as a submicron order in a common process. As steps in a semiconductor manufacturing process proceed, a surface of a base plate becomes more uneven and more complicated. When a fine pattern is formed on the uneven and complicated surface of the plate, the dimensional accuracy is remarkably lowered. That is, the dimensions become smaller in the convex surface portions and larger in the concave surface portions.
In order to overcome this problem, a multilayer resist method has been developed. In this case, for instance, an aluminum film is applied over an uneven semiconductor base plate with an uneven aluminum surface, and then a first photoresist is overlaid on the uneven aluminum film with a flattened photoresist surface. Then, a thin film of a material such as silicon oxides having a resistance against the oxygen plasma is uniformly applied over the flat surface of the first photoresist, and a second photoresist is then evenly formed over the flat surface of the plasma-resistant film. The pattern light exposure and the developing of the second photoresist film are conducted to form the desired pattern thereof with an excellent dimensional accuracy because the surface of the second photoresist film is uniform, and then the etching of the plasma-resistant film is carried out in a certain direction, for example, perpendicular to the flat surface plane of the second photoresist, using the patterned second photoresist as the mask. Next, the first photoresist film is etched in the predetermined direction perpendicular to the flat surface plane of the plasma-resistant film, in the oxygen plasma ashing process using the plasma-resistant film as the mask to form a pattern having a high dimensional accuracy. Further, the etching of the aluminum film laid over the semiconductor plate is performed in the oxygen plasma ashing process using the patterned first photoresist film as the mask with an accurate etched pattern on the uneven semiconductor base plate in the same manner as above.
However, in the aforementioned etching processes using the oxygen plasma, the etched aluminum of the aluminum film is sputtered and attaches to the side walls of the patterned plasma-resistant film, the etched first photoresist and the etched aluminum film during the plasma ashing process.
FIG. 2 schematically illustrates an etching process of an aluminum film 13 applied over an oxide film 12 of a semiconductor base plate 11 using a patterned photoresist 14 laid on the aluminum film 13. In this embodiment, during the reactive ion etching process, a charged particle 16 perpendicularly impacts on the aluminum film 13 to sputter the aluminum film 13, and an etched aluminum spatter 17 attaches to the side walls of the photoresist 14 or the patterned aluminum layer 13a to form aluminum film walls 15 thereon, as shown in FIG. 2a. The aluminum film walls 15 can prevents the attacks of the charged particles and thus plays an important roll to form a precise and fine pattern. However, after the aluminum pattern forming by etching using the photoresist as the mask is finished, the photoresist 14 can be removed by the dry plasma ashing process, but the aluminum film walls 15 cannot be removed, as shown in FIG. 2b.
Such film walls of a material to be etched may be formed regardless of the kind of the material during the dry plasma ashing process. For instance, when a polycrystalline silicon is etched, silicon film walls are formed in the same manner as the aluminum film walls when the aluminum material is etched, as described above. Usually, the aluminum film walls can be removed in the wet chemical etching treatment, for example, using an etching solution including a hydrofluoric acid, but, at the same time, the aluminum pattern and the insulating material of silicon oxide film below the aluminum pattern can also be etched in the etching solution. In the case of the polycrystalline silicon, the gate oxide film under the polycrystalline silicon pattern can be etched as well.
When a halogen radical having a strong reactivity, obtained by activating a gas including halogen element or elements such as fluorine is used for etching, the halogen radical can solely react with the organic compound film to remove it. However, when the photoresist or the gate electrode formed on the silicon or silicon oxide base film is etched by the halogen radical alone, the base film is also etched, and hence the halogen radical alone cannot be used for the etching process. Further, the etching rate of the organic compound film using the halogen radical alone becomes approximately 1000 .ANG./min which is not so quick, in practice.